A single large surface is not a problem in itself. The important thing is how the edges of the surfaces are oriented, how the flat surface is oriented, and whether any part of the edge or surface forms and angle reflector with other parts of the aircraft. Having many surfaces oriented at different angles is a problem, because it becomes difficult to really align them all so they all only reflect only in very few narrowly focused directions. Having many differently oriented surfaces means the aircraft likely have many more directions into which it would reflect any incoming radar beam.
The ventral stabilizers on the j20 is not in itself a problem. Where it becomes a problem compared to the control surface layout of f22 is it presents more surfaces, not bigger surfaces, than on the f22. This is particularly an issue because the ventral surfaces are visible across a wide arc from beneath the aircraft. So the j-20 is likely to possess vulnerable directions to radars searching for it from beneath. While this is an issue, it doesn't necessarily present a crippling issue. If j20's threat warning system is very good in picking up and identifying the direction of threatening radar receivers, and the signals from these warning receivers are integrated into the autopilot to enable the aircraft to always maneuver to direct reflections away from radar emitters, it could become in effect as stealthy from a mission perspective as the f22.
However, if the enemy possesses low probability of intercept radar, or possess radar receivers that are geographically separated from radar emitters, then there is nothing j-20's threat receivers and avionics can do to compensate for its extra number of reflecting surfaces compared to the f22.
Good post. But the problem is everything is all too theoretical and circumstantial.
My point isn't to 'prove' how stealthy the J20 is, because we simply don't have the data to make such a claim. Which is my entire point of easily poking holes in the arguments of those making bold claims about the J20's stealth characteristics with nothing but feelings, vague general principles and other intangibles as back-up.
At the end of the day, you cannot change physics.
If we hold all else equal, a bigger surface will yield a bigger radar return compared to a smaller surface. Same with more surfaces yield higher RCS than fewer surfaces.
But if we are moving goal posts and talking about ground based radar, then all the arguments about the F22 and F35 hiding their horizontal tails behind their main wings also go out the window, since those would also be visible to ground based radar and come into play for RCS.
What we cannot know is how much the RCS will compare with two big sets of surface against 3 much smaller sets, as the aspect towards the planes change.
It would take a massive, detailed dataset; supercomputers and advanced bespoke software to work out the actual RCS difference between a J20's layout and that of the F22/35 from the same radar source from the same angle and as that angle change.
That's why I find all those human eyeball RCS readers so silly and untrustworthy.
I'm no mind reader, but I get the strong feeling the whole reason a lot of the people making bold claims about the J20 are doing so about RCS is also precisely because of how hard it would be to prove it one way of the other - it makes it almost impossible to conclusively call them on their made-up claims.
